The present invention relates to a vibratory screening machine having structure for aligning, sealing and installing the screens rapidly under proper tension.
By way of background, screens require replacement frequently in vibratory screening machines as the screens wear out. In the past, insofar as known, the screens were aligned by eye on the bed of the machine, and this frequently resulted in the screens being improperly located. Additionally, the seals which were used were solid resilient materials which became compressed during machine vibration and lost their sealing capacity. Also, the screens were tensioned by the use of drawbars which were tightened by means of a nut attached to draw bolts which engaged the drawbars. The deficiency of this type of arrangement was that there was no precise way, in the absence of using a torque wrench, for determining how much tensioning force was applied to the draw bolts. This oftentimes resulted in drawbars which were unequally tensioned at various points along their lengths and this caused uneven tension to be applied to the screens. In addition, on a machine having three screens there were usually twenty-four draw bolts. Each draw bolt was tightened by a nut which had to be turned numerous times during both the tightening and loosening procedure. This was extremely time-consuming. Since the flow of material to be screened could not be stopped during the changing of the screens, the longer the time required for changing the screens, the greater was the loss of material which could have been screened. This was particularly critical in the oil drilling industry where the loss of drilling mud which could have been reclaimed was directly proportional to the length of time required to change the screens.